[Bug tree-optimization/112385] `(2 >> a) ^ (5 >> a)` is not optimized to `7 >> a` is 2 and 5 differ in signedness
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112385 Andrew Pinski changed: What|Removed |Added Ever confirmed|0 |1 Last reconfirmed||2023-11-12 Status|UNCONFIRMED |ASSIGNED Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org --- Comment #3 from Andrew Pinski --- Mine, I will handle this.
[Bug tree-optimization/112385] `(2 >> a) ^ (5 >> a)` is not optimized to `7 >> a` is 2 and 5 differ in signedness
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112385
--- Comment #2 from Andrew Pinski ---
We can even do it if we know the unsigned value does not have the last bit set.
That is:
```
int f(int a, unsigned b, int c)
{
b &= 0x;
return (c >> a) ^ (b >> a);
}
```
Note clang(LLVM) does not handle the above.
The way LLVM handles the others is it changes ashift to lshift if the value is
known to be non-negative. But since in the gimple level we are dealing with
types we can't do that in a nice way; RTL level on the other hand yes that can
be done (though nonzero bits is limited there).
[Bug tree-optimization/112385] `(2 >> a) ^ (5 >> a)` is not optimized to `7 >> a` is 2 and 5 differ in signedness
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112385
--- Comment #1 from Andrew Pinski ---
Note a more complex case like:
```
int f(int a, unsigned b, int c)
{
c &= 0x;
return (c >> a) ^ (b >> a);
}
```
Should also be optimized to:
```
int f(int a, unsigned b, int c)
{
c &= 0x;
return (c^b) >> a;
}
```
That is if both are known to be non-negative we can do the combining.
